There are almost 16 million patients with diabetes in the United States; approximately 798,000 new cases are diagnosed each year (1). Among people with diabetes, 15% will experience a foot ulcer in their lifetime. Foot ulcers are a major predictor of future lower-extremity amputation in patients with diabetes. One of the many dangers of pedal ulcers is that they are portals of entry for infection and directly overlie more than 90% of cases of pedal osteomyelitis (a destructive bone disease) (2). About 14-24% of people with a foot ulcer will require an amputation. It is therefore not surprising that diabetes is the leading cause of non-traumatic lower-extremity amputations in the US. Despite much effort directed toward amputation prevention in the last decade, the incidence of lower-extremity amputation in people with diabetes continues to rise (3). The cost of diabetic foot ulcers is at least $1 billion annually in the United States (4). In a study done by Ramsey, S. D. et al at the Group Health Cooperative of Puget Sound, the attributable cost associated with a foot ulcer was $28,000.00 per patient in the two years following diagnosis (5).
Unfortunately, the mortality rate for amputees is very high and constantly increasing. If there were a diagnostic tool that could be used as a warning device for those patients that suffer from the loss of protective sensation caused by peripheral neuropathy, many diabetics could return to a more “normal” lifestyle. It is well known that unrecognized trauma has gives rise to most of the foot problems that this group of individuals suffer from. Development of a device that could be used on a daily basis by the patient that would provide the patient with feedback to inform them about when they are at risk would be very valuable.
One of the largest tasks in the development of such a tool is to find what characteristics of diabetic feet are indicators of the condition of the individual's feet. Commonly, pressure has been and remains to be an important indicator of ulceration (6, 7, 8, 9). In-shoe pressure, unfortunately, is a difficult and expensive parameter to measure. There are some pressure-sensing devices available such as the Novel/EMED insoles and the Tekscan F-scan. Neither of these systems meets the desired goal of making the patient completely independent and aware of their foot condition at any time. The Novel insole starts at $10,000.00 for the entry-level variety. The Tekscan insole is cheaper but requires a much more bulky data acquisition system. The Tekscan insoles are designed for a small number of cycles. After a few uses, they lose their ability to accurately determine the pressure.
Temperature, which is very closely associated with pressure, is a much more reliable parameter to measure. This is based, in part, on the available hardware. Thermistors that are highly accurate and also very small are readily available. However, less attention has been paid to plantar temperatures as an indicator of ulcer risk as compared to pressure (10, 11, 12).
U.S. Pat. No. 6,195,921 describes a device that measures pressure of predetermined pressure points of the foot using a flexible sensor mat, and also measures the temperature inside the shoe. U.S. Pat. No. 5,642,096 contains pressure and temperature sensors in a liquid hydrocell within an insole to detect the pressure and temperature values of a patient's feet. U.S. Pat. No. 5,929,332 describes a sensor shoe with a plurality of sensors which measure pressure, temperature, moisture of feet and activates an alarm if values exceed a preset threshold. US patent application 2005/0060906 describes shoes which pump hot air and odor out and fresh air in, which pumps are controlled by an electronic temperature control unit on the outside of the shoe.
Clinically, patients with the loss of protective sensation and failing eyesight are asked to monitor their own feet between visits to their podiatrist. Sadly, many patients are presented to the emergency room after reaching a point of no return in regard to their feet. Currently, there is no device available that can provide a portable and continuous monitoring and assessment of the condition of the feet in diabetic patients. Such a device is urgently needed.